For me, it started with a family friend I had as a babysitter for a long time as a kid. Shiny, soft, thick, straight blonde hair that went past her waist. She would let me brush and play with her hair while she watched TV or did homework or whatever else, and occasionally she'd play with me by whipping it in my face or tickling me with it. Had her as a sitter from about ages 8 to 11 before she moved away. I still talk to her every now and then, but her hair isn't quite as long anymore, maybe a few centimeters above the small of her back.